Thread: Dark Energy Idea

This is a little fantastical but maybe worth a bit of consideration (these are the things that pop in my head as I drift off to sleep XD): I'm sure you've all seen the "bowling ball on trampoline" analogy of gravity; could it be possible that dark energy is a mass on the "other side" of the trampoline (universe)? As the Bowling ball on side A of the trampoline pulls marble A too it, marble B on Side B would be repelled. Perhaps, and this is a pretty big perhaps, what we experience as dark energy in our universe is just regular ol gravity in the universe next door and vice versa.

MODERATOR NOTE : Welcome to The Physics Forum, drwelch. I have moved your post here, since this section is specifically designed to host topics which are speculative or hypothetical in nature. You are free to discuss your idea/question here. Welcome again, and do let me know if you have any concerns.

very warm from you markus,i admire that. drewlch am not sure if you question is clear enough.please make it straight.

It's really hard to explain without pictures and wild hand gestures, but I'll try XD. Look at this video: https://www.youtube.com/watch?v=p59QMpbu1Ao To see what I'm talking about you would move the sun model below the plane so the plane bulges up instead of down, pushing the little earth model out instead of in. I hope that makes sense.

I did'nt watch your video,did'nt want to. Buh i think you are saying that as everything attracts everything-else,then dark energy is a mass pulling our universe. Buh dark energy is an hypothetical energy we believe is pushing the galaxies apart,whence,gravity that was suppose to slow the expansion cannot. Theres no dark energy without dark matter so its not that dark energy might be a matter,its a potential energy affecting the movement of galaxies and universe,produced by dark matter. When u agree that i understand what you are trying to say,then we can talk about your idea.

Originally Posted by drwelch

This is a little fantastical but maybe worth a bit of consideration (these are the things that pop in my head as I drift off to sleep XD): I'm sure you've all seen the "bowling ball on trampoline" analogy of gravity; could it be possible that dark energy is a mass on the "other side" of the trampoline (universe)? As the Bowling ball on side A of the trampoline pulls marble A too it, marble B on Side B would be repelled. Perhaps, and this is a pretty big perhaps, what we experience as dark energy in our universe is just regular ol gravity in the universe next door and vice versa.

It's an interesting speculation. Yet, I wouldn't say it's logically sound. The rubber sheet analogy is just that, an analogy. It's there to help visualize the notion of massive objects "curving" spacetime. As far as I know, it's far from a true physical representation by theory. So I doubt the practicality of basing ideas off of it.

However, if I'm not mistaken, the universe is modeled as a 4-dimensional spacetime manifold. Though a simple visualization might not yield anything satisfactory, one can certainly find profound implications working with the math describing it.

Originally Posted by epidecus

It's an interesting speculation. Yet, I wouldn't say it's logically sound. The rubber sheet analogy is just that, an analogy. It's there to help visualize the notion of massive objects "curving" spacetime. As far as I know, it's far from a true physical representation by theory. So I doubt the practicality of basing ideas off of it.

However, if I'm not mistaken, the universe is modeled as a 4-dimensional spacetime manifold. Though a simple visualization might not yield anything satisfactory, one can certainly find profound implications working with the math describing it.

Spacetime, in general relativity, is indeed a 4-dimensional Lorentzian manifold. That is pretty well known. The issue with dark energy is the accelerating expansion of 3-dimensional spacelike slices of that manifold. That expansion is accurately modeled using general relativity.

The model (often called the model) requires the use of a small positive cosmological constant in the Einstein field equations. No one has a clue as to what phenomena might produce this constant.

One attempt to explain the positive cosmological constant is via the energy of the quantum vacuum. That energy results in a negative pressure term in the stress-energy tensor of general relativity that is equivalent to a positive cosmological constant. Unfortunately calculations based on quantum electrodynamics over-predict the observed cosmological constant by 120 orders of magnitude, which is possibly the largest theoretical error in the history of physics. Wilczek has described this as the most important outstanding problem in elementary particle physics.

The mystery remains as to what phenomena could produce a cosmological constant of the observed magnitude (it is small).

Originally Posted by drwelch

This is a little fantastical but maybe worth a bit of consideration (these are the things that pop in my head as I drift off to sleep XD): I'm sure you've all seen the "bowling ball on trampoline" analogy of gravity; could it be possible that dark energy is a mass on the "other side" of the trampoline (universe)? As the Bowling ball on side A of the trampoline pulls marble A too it, marble B on Side B would be repelled. Perhaps, and this is a pretty big perhaps, what we experience as dark energy in our universe is just regular ol gravity in the universe next door and vice versa.

The bowling ball/trampoline analogy does at least as much damage as it does good. In this case the analogy is obviously misleading you. It just doesn't work that way.

Originally Posted by merumario

....Theres no dark energy without dark matter so its not that dark energy might be a matter,its a potential energy affecting the movement of galaxies and universe,produced by dark matter. .......

I don´t understand this...dark matter and dark energy are proposed (and unknown) independent concepts...just to explain different observations that we don´t understand nowadays.

It is not true that dark energy is produced by dark energy... but yes coud be produced for external (of Our Universe) matter attraction...or by external vacum (?)

Originally Posted by merumario

Theres no dark energy without dark matter so its not that dark energy might be a matter,its a potential energy affecting the movement of galaxies and universe,produced by dark matter. When u agree that i understand what you are trying to say,then we can talk about your idea.

The dark matter hypothesis is quite a bit older than the dark energy hypothesis, and the two have very little, if anything to do with one another.

Dark matter was proposed by Oort and Zwicky in the early 1920's as a means to account for an observed anomalous rotation rate of galaxies, including the Milky Way. Essentially the visible mass is not sufficient to provide the gravitational attraction necessary to explain the observed rotation rate of the outer portions of galaxies. Quite a bit of additional evidence has since been found to support the hypothesis that a great deal of the mass in the universe is thus far undetected. No one knows what dark matter is,although there is a lot of speculation as to what it might be.

Dark energy, as a hypothesis, is of much more recent origin. In the late 1990's observations of Type IA supernovas provided evidence that not only is the universe expanding, but in fact the rate of expansion is increasing. Until that rather surprising bit of data was obtained it was generally believed that the expansion of the universe was decreasing due to the ordinary action of gravity. "Dark energy" is the name given to whatever is creating what is essentially a repulsive effect. It is even more of a mystery than is dark matter.

While there is some responsible speculation as to what dark matter might be, (supersymmetric particles, cold dark objects in space, black holes, other stuff), no one has a clue what dark energy might be. It can be modeled as a positive cosmological constant in the Einstein field equations, but no one has any good candidate for what might produce such a constant. The attempt to explain it in terms of the vacuum energy of space, calculated using quantumn electrodynamic, failed as it over-predicts the obseved effect by a factor of , which is probably the largest discrepancy between theoretical prediction and observation in the entire history of physics. No one knows why -- Wilzcek has called this the most important outstanding problem in particle physics.

The key point here is that dark matter and dark energy have essentially nothing to do with each other, and their effects are as close to the opposite of one another as one might desire. Dark matter is associated with ordinary gravity. Dark energy is associated with a universal repulsive effect.

Originally Posted by DrRocket

The bowling ball/trampoline analogy does at least as much damage as it does good. In this case the analogy is obviously misleading you. It just doesn't work that way.

This is probably a slightly better way to try and visualize it ( still just an analogy though ! ) :

http://static.ddmcdn.com/gif/videos/480x360/29805.jpg

Originally Posted by Markus Hanke

This is probably a slightly better way to try and visualize it ( still just an analogy though ! ) :

http://static.ddmcdn.com/gif/videos/480x360/29805.jpg

That doesn't do much for me.

The best way that I know to visualize curvature of spacetime (and it not just space that is curved) is to imagine two balls in the space shuttle orbiter as it orbits the earth being released a short distance apart. They will slowly separate -- think of tidal influences -- but as they are in free fall, each describes a geodesic in spacetime. Spacetime curvature is manifested by this divergence of geodesics.

Note that the path followed by an object in orbit is a geodesic in spacetime. But it is also an ellipse in space, and that ellipse is most certainly not a geodesic in space. If you think about this a minute or two, it will become clear just how bad the bowling ball/trampoline analogy really is.

The "analogies" that one sees in pop science pieces, at least to me, completely fail to convey the meaning of spacetime curvature and how it is reflected in gravitation. That ought to be expected since the notion of curvature is not what one might naively expect -- for instance and ordinary right circular cylinder is flat. It is not hard to construct a flat torus or a flat Klein bottle either. Moreover, all curves are flat (no matter how complex the squiggle might appear. Curvature does not mean what many people think it means.

There is just no getting around the fact that differential geometry requires one to think abstractly and to absorb a great deal of material simply to understand the definitions.

I know of zero popularizations of general relativity that get across the real meaning of spacetime curvature or gravitation, and even some physics books aimed at beginning and intermediate levels are not very satisfying. Yet people read this pop-sci stuff and think they understand the theory well enough to argue the matter. This is a case of failing to understand that one does not understand, and to a large degree it is the fault of the pop-sci authors for giving an impression of understanding while skirting critical issues and concepts. The profit motive has intruded on the market for expositions of advanced physics, and the result is a lot trash science. One must be very careful, critical and skeptical when reading popularizations. I personally reccommend reading only stuff written by the A-list (Feynman, Weinberg, Wheeler, ''tHooft, Hawking, Thorne, etc.) and even then with a critical eye. Better yet is to at least supplement popularizations with real science texts and papers -- the x-rated stuff -- still written by masters of the subject. When professionals are writing for professionals they can't and don't get away with some of things that you see in the popular literature.

Dr Rocket ... you give a very good explanation about what we know (mainstream) abuot DARK Energy and Matter....

...But for me both (DARK Energy and Matter) are a clear demostration that our current knowledge (paterns, models, theories,...) about the Universe is not completed...and we need these concepts to try to puzzle them.

I am sure that in futures wide models these concepts will fit better.... but should be made an important conceptual jump

Possibly, to understand these two concepts...we have to be able to conceive them within a wider scale spectrum that we know nowadays...and to puzzle them whithin higher model... as it was to understand that the Earth is spherical ... 1000 years ago scientifics tried to explain the movement of the moon, sun, planets and stars....by complex astrolabes !!!

Originally Posted by dapifo

Dr Rocket ... you give a very good explanation about what we know (mainstream) abuot DARK Energy and Matter....

...But for me both (DARK Energy and Matter) are a clear demostration that our current knowledge (paterns, models, theories,...) about the Universe is not completed...and we need these concepts to try to puzzle them.

I am sure that in futures wide models these concepts will fit better.... but should be made an important conceptual jump

Possibly, to understand these two concepts...we have to be able to conceive them within a wider scale spectrum that we know nowadays...and to puzzle them whithin higher model... as it was to understand that the Earth is spherical ... 1000 years ago scientifics tried to explain the movement of the moon, sun, planets and stars....by complex astrolabes !!!

There is a great deal that is not known. Physics is not a moribund discipline, but rather is a vibrant area of research. It is likely to remain so for a long time.

Research requires imagination. But that imagination must be used within the very strict confinement imposed by the body of empirical and observational data that supports the current theories, within their known domains of validity. New theories must not contradict that data, and hence to have any chance of being valid must agree with established theories in those situations in which those theories have been shown to be accurate approximations to reality. This requirement is called the "coorespondence principle", but it is really nothing more than the requirement that any valid theory must not be contradicted by what is actually observed.

I have no doubt that a future explanation of dark energy or dark matter will require a significant extension of the Standard Model or general relativity or, more likely, both. But there is no such theory currently on the table, ready to be challenged by experiment, or indeed any mathematically well-defined and consistent theory at all. What does exist is a great deal of ongoing research by some very talented people, but nothing that is yet ready for prime time.

The remaining problems are extremely complex, sufficiently so that any clear rigorous explanation of the issues requires mathematics that is well beyond what one can expect of a layman, or indeed even a non-specialist scientist. All attempts by even the best specialists have thus far fallen short of any testable explanations or even mathematically rigorous derivations and predictions. Dark energy and dark matter are certainly included in the list of remaining problems.

In short, this is really hard stuff.

OK ... I will try to explain what I mean by "jump scale".

I hope you are receptive ... and try to understand the "global concept" of what I will expose ... that does not contradict any of the current science ... and this is just a different way of seeing the universe.

Imagine you "a" humanity with a technological level similar to "our" living inside an atom, ... on an electron (10 ^ -20 meters) circling the nucleus ... The spectrum of scale that would control would be 10 ^ -50 to 10 ^ +10 meters ... while ours is 10 ^ -30 to 10 ^ +30 meters.

For them it would be more understandable this microscopic universe than ours .... surely could better understand what lies beyond the Planck scale ... but it would make much more complicated to understand that there are galaxies ... or Big-bang itself ...

It all depends from Spectrum Scale from which we look.

If we could see "Our Universe" from outside its limits (f.e. from a scale of 10^+50 meters), it may be easier to understand the why and the cause of the Energy and Dark Matter.

Please note that there has been of change of forum rules - with immediate effect, The Physics Forum no longer permits the presentation and discussion of personal theories which are not based on current scientific understanding :

http://www.thephysicsforum.com/annou...e-changes.html

This thread is therefore now locked.